1. Field of Invention
This invention relates to a low-temperature, liquid phase injection molding process for polyethylene.
2. Brief Statement of the Prior Art
Thermoplastics, particularly polyethylene, are widely used in various molding operations, including rotational molding, blow molding and injection molding. All these processes have some limitations, such as the inability of rotational and blow molding to produce products with reinforced wall areas and the high cost of injection molding equipment which precludes use of this process to produce limited quantities of product.
Some specialized molding processes have been developed for specific resins, such as reaction injection molding wherein an organic polydiisocyanate and a polyol are injected into a mold cavity for reaction therein. Another process is liquid injection molding in which liquid silicon rubber and a catalyst are mixed and metered into a mold cavity. Resin transfer molding is another process which uses a two-part epoxy formulation which is mixed and injected into a mold cavity which is usually loaded with a preformed fiber reinforcement. These specialized processes use thermosetting resins which react and are cured in the mold. Heretofore no process has been developed to permit low-temperature, liquid-phase injection of thermoplastic resins, particularly polyethylene-containing resins, into a mold which is heated to solidify the resin within the mold.
Heretofore there has been no method for the low-temperature liquid phase injection molding of polyethylene, a method which would permit use of low cost molding equipment useful for specialized, low volume manufacture and for molding parts in which temperature sensitive elements such as electronic components are encapsulated.